The present invention relates to block polymers composed of chemically combined blocks of aromatic polyformal oligomer and aromatic polycarbonate and method for making such materials. A mixture of an aromatic oligomeric polyformal and a bisphenol is phosgenated and the block polymer is recovered from the resulting mixture.
Prior to the present invention, aromatic polycarbonates were generally recognized as high impact thermoplastics. As shown by Barclay U.S. Pat. No. 3,069,385, aromatic bisphenol used in the production of polycarbonates, can be modified with formal linkages. The resulting aromatic polyformal oligomer was then phosgenated to produce thermoplastic materials exhibiting reduced softening temperatures as compared to conventional aromatic polycarbonates. However, the softening temperatures of the polyformal carbonates of Barclay were often below 100.degree. C. which eliminated their use in a variety of applications.
An alternative method for modifying aromatic bisphenols of the formula, EQU HOROH, (1)
with formal linkages is shown in copending application of Allan S. Hay, Ser. No. 889,393, filed Mar. 23, 1978 and assigned to the same assignee as the present invention, where R is a divalent C.sub.(6-30) aromatic organic radical. As shown by Hay, aromatic polyformal oligomers are made by effecting reaction between a bisphenol of formula (1), a methylene halide in the presence of a base and an organic solvent which can result in the production of a mixture of the polyformal oligomer and cyclic polyformal. Although the phosgenation of such mixture can result in aromatic polyformal carbonate having improved heat-distortion characteristics as compared to conventional aromatic polyformals, the presence of cyclic polyformal can interfere with the utility of such film forming materials.
Improved results over Hay are provided by the method of Loucks and Williams as shown in copending application Ser. No. 889,397, filed Mar. 23, 1978 assigned to the same assignee as the present invention, whereby reduced cyclic polyformal content in the linear aromatic polyformal is achieved by a filtration of the reaction product of the bisphenol and methylene halide in the presence of a base, followed by the addition of an antisolvent to the reaction mixture to effect reverse precipitation.
In copending application Ser. No. 942,952 of James C. Carnahan, filed Sept. 18, 1978 and assigned to the same assignee as the present invention, polyformal carbonates having an improved glass transition temperature sufficient to raise the heat distortion temperature of the polymer allowing it to be used in applications requiring 100.degree. C. sterilization are provided by the employment of an aromatic bisphenol dimer in place of the aromatic polyformal oligomer of the prior art. A further rise in heat distortion temperature is achieved by phosgenating a mixture of such bisphenol formal dimer and additional bisphenol of formula (1) to produce aromatic polyformal carbonates having aromatic polycarbonate blocks chemically combined with bisphenol formal dimer groups. However, the procedure of Carnahan requires the production of the bisphenol formal dimer which is based on the use of monocapped bisphenoxide salt of copening application of James C. Carnahan, Ser. No. 942,957, also filed concurrently herewith and assigned to the same assignee as the present invention.